PIK3CA and breast cancer: Specifically, mutations in KRAS, BRAF, or phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) were detected in CTCs but were absent in the primary tumors [40,41], suggesting a potential role in resistance to molecularly targeted therapies [42,43].Similarly, in luminal-type breast cancer, certain activating mutations are detected specifically in CTCs but are absent in the primary tumor.